There's Cino, but that's in Montana and I've heard that it has more gravel than Eroica. I did pose this exact same question about seven years ago and someone on the forum responded "why don't you organize one". So I did, and got about a dozen takers to ride Old Tunnel Road, Redwood Road and Pinehurst Road in Berkeley/Oakland. Subsequently I've become friends with several of those folks and we ride about once a week and once a year usually ride what we call "Marinica" which is a primarily vintage ride in Marin a week or so before Eroica. Note that these rides typically only have between 2 and 5 people so they're probably not exactly what you're looking for.